Who among us doesn't have a rough day from time to time? You know the type of day I'm talking about. That wearisome sort of day. The kind of day where wit, inspiration and motivation are all reached for in earnest, only to be found in equally short supply.

Well, perhaps you'll take as much comfort as I did in stepping back and remembering that even the most gifted among us have days that feel bleak, wearisome and uninspired. "Days when they feel dumb," as NPR's Robert Krulwich puts it. "Really, really dumb."

On October 1, 1861, Charles Darwin was having precisely such a day, when he wrote to friend and fellow scientist Charles Lyell the words you see up top. "I am very poorly today and very stupid and hate everybody and everything. One lives only to make blunders." (It bears mentioning that Darwin penned these words just two years after the remarkably successful publication of On the Origin of Species.)

We're not reveling in Darwin's sentiments, here. We mean only to remind you that even the brightest among us have crummy days. Try to remember that the next time your brain just doesn't seem to be working — that all the way back in 1861, Charles Darwin, of all people, was scribbling bitterly at a sheet of parchment, feeling the exact same thing.

Read more on Darwin's "Terrible, Horrible, No Good, Very Bad Day" — including scans of the original letters, written in Darwin's hand — over at Krulwich Wonders.